The relationship between endometrial thickness and outcome of medicated frozen embryo replacement cycles.

To examine the relationship between endometrial thickness and outcome of medicated frozen-thawed embryo replacement (FER) cycles.A retrospective observational study.Assisted conception unit at a university hospital.All patients who underwent an FER cycle between 1997 and April 2006 and met the inclusion criteria.For endometrial preparation, a daily dose of 6 mg of oral E(2) valerate was started on menstrual day 1, and P pessaries (800 mg daily) were administrated when the endometrial thickness had reached 7 mm or more, with ET taking place 2-3 days later. The FER cycles were categorized according to endometrial thickness measurement on the day of P supplementation.Implantation, clinical pregnancy, ongoing pregnancy, and live birth rates.In all, 768 consecutive medicated FER cycles were analyzed. The lowest pregnancy rates were associated with endometrial thickness <7 mm (n = 13) and >14 mm (n = 12; 7% in both groups). Significantly higher implantation (19% vs. 12%), clinical pregnancy (30% vs. 18%), ongoing pregnancy (27% vs. 16%), and live birth (25% vs. 14%) rates were achieved in cycles where endometrial thickness was 9-14 mm (n = 386), compared with those in which endometrial thickness was 7-8 mm (n = 357). These differences remained significant after adjusting for confounding variables (adjusted odds ratio [OR] = 1.83 [confidence interval {CI} = 1.3-2.6] for clinical pregnancy, 1.8 [CI = 1.2-2.6] for ongoing pregnancy and 1.9 [CI = 1.3-2.8] for live birth).In medicated FER cycles, an endometrial thickness of 9-14 mm measured on the day of P supplementation is associated with higher implantation and pregnancy rates compared with an endometrial thickness of 7-8 mm.